Light projected from an active lighting means to an object is reflected by the object, and a light spot is produced on a light-sensitive element by the light reflected from the object. The distance to the object is determined by detecting the position of the light spot on the light-sensitive element. The light-sensitive element for receiving the reflected light from the object has formed on a portion of a surface thereof an insensitive zone which has the same width or the same area as the light image produced by the reflected light and the light-sensitive element moves on an image plane in a certain relationship with the distance to the object whereby a change in a photoelectric output of the light-sensitive element is detected to detect the distance to the object.

An active type range finder has a light-emitting element which is pulsatively driven to project light pulses on an object to be photographed. A photodetector element receives the light reflected from the object and produces a photoelectric output signal proportional to the amount of received light. A light-shielding member is scanned over the light-sensitive surface of the photodetector element in correlation with the distance to the object so that the light-shielding member successively shields successive areas of the light-sensitive surface from receiving light. An a.c. amplifier amplifies the photoelectric output signal, and an integrating circuit integrates the amplified photoelectric output signal and produces an integrated d.c. signal having a negative peak value indicative of the position of the scanning light-shielding member which corresponds to the object distance. Detecting circuitry detects the negative peak value and provides a corresponding detection signal indicative of the object distance.

Light projected from active lighting means or light projecting means toward an object is reflected by said object and a light spot is produced on a light sensitive element by the reflected light. A distance to said object is determined by sensing a position of said light spot. When a shade detector scanning the surface of the light sensitive element shields the light spot generated by the light reflected from the object, a photoelectric output from said light sensitive element is varied. Correspondence between the position of said shade detector when said photoelectric output is varied and a distance to said object enables a measurement of the distance to said object.

An arrangement for 3-D optical measurement systems employing scanned light beams or planes. A lens used to image projected light that is reflected from a measured surface, is moved onto a light-sensitive detector. The lens movement is coordinated with the movement of the projected light beam or plane to assure that the image on the detector remains in sharp focus at all times. The sharp focus is maintained by moving the detector in coordination with the movement of the projected light beam or plane, or by changing the effective optical path lengths to the detector in coordination with the movement of the projected light beam or plane.

A distance detector capable of measuring the distance between the range detector and an object by directing a light emitted from a light emission element to the object and receiving the reflected light and advantageously adaptable particularly to small-sized cameras. The light reflected on the object is received by a single light-receiving element. The reflected light is condensed by a condenser and concentrated on the light-receiving element. The light-receiving element comprises an element, for example a photopotentiometric element, varying in the electric output according to the position of the light spot of the reflected light. The output of the element in the form of electric signal continuously varies in proportion to the distance between the range detector and the object.